The present invention relates to an improved mill feeder roll to be used in combination with another roll for force-feeding a mill of the type generally employed for grinding a material, such as sugar cane and the like, while contributing in pre-extracting and draining juice therefrom, thereby leaving a drier material to be force-fed into the mill by the rotating action of the rolls.
As is known in the sugar industry, the purpose of a cane mill is to grind sugar cane while extracting and recovering a maximum of juice therefrom. A conventional cane mill comprises basically a top roll and a bottom roll, the two rolls rotating in directions such that a blanket of sugar cane being nipped therethrough is ground. Sucrose extraction is achieved in conventional cane mills by providing "messchaert" grooves in the bottom rolls such that, as the blanket is nipped and ground between the two rolls, the sucrose juice is drained downwardly through the messchaert grooves. The mill top roll is mounted on a shaft supported in split bearings, the top half of each of which is subjected to hydraulic pressures acting downwardly thereon. The top roll can thus move up and down, depending on the thickness of the blanket of cane being nipped. An inherent disadvantage of such conventional cane mills, however, is the fact that a substantial amount of the extracted juice invariably becomes trapped in the upper part of the cane blanket, thereby causing reabsorption during passage of the incoming cane blanket between the rolls. Such reabsorption is quite undesirable, because it not only impairs the overall extraction of the mill but also its "feedability", and thus its capacity, through slippage of the roll surfaces against the wet cane. With a view of improving mill feedability, mill feeder rolls are now being used on most cane mills. The purpose of a mill feeder roll is to work in combination with another roll, generally the mill top roll, such that a blanket of cane being fed to the mill is first nipped between the two rolls, thereby causing pre-extraction of part of the juice contained in the cane, prior to the blanket of cane being force-fed into the mill by the rotating action of the rolls. Yet, because conventional mill feeder rolls do not have provision for draining the pre-extracted juice, their use, although improving somewhat the feedability of the mill, does not solve the problem of juice reabsorption by the incoming blanket of cane. In fact, because of the additional amount of juice extracted by this method, more juice becomes trapped in the upper part of the cane blanket.
To alleviate this disadvantage, a mill top roll having an internal drainage system has been devised which substantially improves the performance of a mill, by draining most of the juice which would otherwise become trapped in the upper part of the cane blanket. Such a roll is disclosed in U.S. Pat. No. 4,391,026. However, this type of roll is quite expensive to manufacture, due to its sophisticated design and the fact that it has to be necessarily of very heavy construction in order to be able to lift against the considerable pressures (usually 65 to 70 tonnes per foot of roll length) to which its bearings are subjected during operation.
In the light of what has been dicussed above, it becomes apparent that the ideal solution for overcoming the above noted disadvantages would be to provide an improved mill feeder roll of relatively light and inexpensive construction, which would have the additional capability of draining part of the pre-extracted juice, while contributing in force-feeding the mill with a drier blanket of cane.